KR100843252B1 - Iterative reception method and Iterative receiver - Google Patents

Abstract

The present invention relates to a repeating reception method and a repeating receiver in a mobile communication system.

The present invention uses the hard decision value of other cells except for the self cell to remove the inter-cell interference in the received signal repeatedly received in the multi-cell environment. In addition, the hard decision value of the self-cell signal is used to remove interference of other users in the self-cell which may occur due to inaccuracy of the channel estimation. In addition, in order to improve reception performance of the repeated receiver performing interference cancellation using the hard decision value, the channel estimate is updated by repeatedly performing channel estimation on the repeatedly received signal using the hard decision value of the self-cell signal.

MC-CDMA, multicarrier, hard decision, interference, repeated reception

Description

Iterative reception method and Iterative receiver

1 is a structural diagram illustrating a repetitive receiver in an MC-CDMA system according to a first embodiment of the present invention.

2 is a structural diagram showing an equalizer according to a first embodiment of the present invention.

3 is a flowchart illustrating an iterative receiving method including an interference cancellation process in an MC-CDMA system according to a first embodiment of the present invention.

4 is a flowchart illustrating an example of a despreading, hard decision, and redistribution process according to a first embodiment of the present invention.

5 is a structural diagram illustrating a channel estimator according to a first embodiment of the present invention.

6 is a flowchart illustrating a channel estimation method to which an EM algorithm is applied during an iterative reception process according to a first embodiment of the present invention.

7 is a structural diagram illustrating a repetitive receiver in an MC-CDMA system according to a second embodiment of the present invention.

8 is a flowchart illustrating an iterative receiving method including an interference cancellation process in an MC-CDMA system according to a second embodiment of the present invention.

9 illustrates an operation of canceling intra-cell and inter-cell interference according to a second embodiment of the present invention.

The present invention relates to a repeating reception method and a repeating receiver in a mobile communication system, and more particularly, to a repeating reception method and a repeating receiver for removing interference from a received signal repeatedly received in a multi-cell environment.

In a mobile communication system such as a Multi-Carrier-Code Division Multiple Access (MC-CDMA) system, interference between user symbols in a cell can be effectively eliminated or avoided due to the orthogonality of spreading codes. However, it is not easy to effectively eliminate or avoid interference between cells in a multi-cell environment. Such inter-cell interference greatly hinders the mobility and stability of the mobile communication system at the cell boundary region. Particularly, a terminal accommodating multiple reception antennas in a downlink of an MC-CDMA system can relatively easily inter-cell interference by using space-time diversity, compared to a terminal having a single reception antenna. Inter-cell interference cancellation is a challenge.

In particular, a method for removing such inter-cell interference in MC-CDMA systems has not been actively studied to date. In order to remove such inter-cell interference in MC-CDMA system, [P. L. Kafle and A. B. Sesay, "Iterative semi-blind multiuser detection for coded MC-CDMA uplink systems", IEEE Trans. Comm., Vol. 51, pp. 1034-1039, July 2003], a repetitive reception scheme based on the proposed minimum mean squared error (MMSE) multiuser detection (MUD) has been proposed. Since the number of carriers (for example, 1024) or the inverse of a matrix having a dimension of an arbitrary spreading element must be calculated for each symbol, there is a problem of considerable complexity.

In order to solve this problem, the present invention provides an iterative reception method and a repeater receiver for removing intra-cell and inter-cell interference in a multi-cell environment.

In addition, the present invention provides a repetitive reception method and a repeater receiver for effectively removing intra-cell and inter-cell interference while having low complexity in a terminal using a single antenna in the downlink of a mobile communication system.

In a multi-cell environment according to an aspect of the present invention for achieving the above object, a receiving method in which a receiver repeatedly receives a received signal including a first cell signal and at least one other cell signal,

Hard determining each cell signal included in the received signal and outputting a hard decision value corresponding to each cell signal; And estimating the inter-cell interference signal using the remaining hard decision values other than the hard decision value corresponding to the first cell signal among the hard decision values, and removing the inter-cell interference signal from the received signal. .

In addition, in a multi-cell environment according to another aspect of the present invention, a repeating receiver for repeatedly receiving a received signal including a first cell signal and at least one second cell signal,

A first hard determiner for hard determining the second cell signal and outputting a first hard decision value; And an inter-cell parallel interference canceller for estimating the inter-cell interference signal using the first hard decision value and removing the inter-cell interference signal from the received signal.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it may further include other components, except to exclude other components unless otherwise stated. In addition, the terms "...", "...", "block", etc. described in the specification mean a unit that processes at least one function or operation, which is hardware or software or a combination of hardware and software. Can be implemented.

Now, a repeating reception method and a repeating receiver in which a terminal using a single receiving antenna removes inter-cell interference in a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the drawings, taking an MC-CDMA system as an example. do. In the embodiment of the present invention, the MC-CDMA system is described as an example, but the present invention can be applied to other mobile communication systems such as orthogonal frequency division multiplexing (spread-OFDM).

Meanwhile, in a mobile communication system according to an embodiment of the present invention, a subcarrier position allocated to a specific receiver to receive a signal from multiple cells located at a cell boundary and perform inter-cell interference cancellation through repeated reception accordingly is all cells. Are equally assigned. On the other hand, this applies only to a receiver located at a cell boundary that requires intercell interference cancellation, and does not apply to a receiver located in a cell center that does not require intercell interference cancellation. In addition, in a mobile communication system according to an embodiment of the present invention, in a multi-cell environment, a receiver includes information on a modulation scheme of all cell signals such that a receiver performs not only a signal transmitted from a specific cell but also a signal transmitted from another cell. Allocates a control channel.

)는 다음의 수학식 1과 같다. First, look at with respect to the MC-CDMA system model used in the embodiment of the present invention, the Q of the multi-cell environment of the L subcarriers and L the diffusion element, and the q-th cell of the MC-CDMA system with K _q users Transmission signal

) Is shown in Equation 1 below.

는 q번째 셀의 k번째 사용자의 확산코드와 셀 구분을 위한 스크램블 코드의 곱을 의미하고,

는 송신 심볼을 의미한다. q번째 셀의 직교 확산 행 렬을

로 놓으면,

가 된다. 또한, q번째 셀의 송신신호의 l번째 부반송파 신호

의 에너지는

로 가정한다. 한편, 단말의 수신기에서 수신되는 주파수 영역의 수신 신호 벡터(

)는 다음의 수학식 2와 같다. here

Denotes the product of the spread code of the k th user of the q th cell and the scramble code for cell division,

Denotes a transmission symbol. Orthogonal Diffusion Matrix of the qth Cell

If you put it on,

Becomes In addition, the l- th subcarrier signal of the transmission signal of the q- th cell

The energy of

Assume that Meanwhile, the received signal vector of the frequency domain received by the receiver of the terminal (

) Is shown in Equation 2 below.

는 채널 행렬을 의미하고,

와 같이 나타낼 수 있다. 또한,

는 사용자 신호이고,

은 잡음 벡터를 나타낸다. here,

Means channel matrix,

Can be expressed as: Also,

Is a user signal,

Denotes a noise vector.

In the received signal of Equation 2, interference between user symbols in a cell can be effectively removed by despreading after orthogonality of a channel with a single tap equalizer in a frequency domain. On the other hand, since the orthogonality of each cell's scramble code is not guaranteed, inter-cell interference is not removed from the received signal.

Now, with reference to the MC-CDMA system model described above, a repeating receiver for removing the inter-cell interference of the terminal using a single antenna in the MC-CDMA system according to the first embodiment of the present invention will be described in detail. .

Meanwhile, in the first embodiment of the present invention, a single tap MMSE equalization using a minimum mean squared error (MMSE) as a channel equalization reference in a single tap equalizer used to remove interference between user symbols in a cell. The use of the group will be described as an example.

FIG. 1 is a structural diagram illustrating a repetitive receiver in an MC-CDMA system according to a first embodiment of the present invention, and shows an example of a structure of a repetitive receiver when receiving signals from two cells.

A repeating receiver according to an embodiment of the present invention configures a separate interference cancellation path for each cell in order to remove intercell interference. For example, as shown in FIG. 1, when two cell signals are received, the repeater receiver performs interference cancellation on the signals of the first cell and the second cell through the first cell path and the second cell path, respectively. This is because the hard decision of another cell signal used to remove intercell interference from the cell signal that the repeater receiver should receive is calculated using the signal from which the intercell interference is removed from the other cell signal. This is because it is necessary to remove the interference.

Meanwhile, FIG. 1 illustrates a case in which two interference cancellation paths exist by receiving signals from two cells to explain the first embodiment of the present invention. However, this does not limit the present invention, and the number of interference cancellation paths may vary according to the number of cell signals received by the repeater receiver of the terminal in a multi-cell environment. .

In the following description, a repeater receiver of an MC-CDMA system is widely known as an Discrete Fourier Transform (DFT) device and a cyclic prefix remover. If so, the description of the basic receiving apparatus that can be easily executed is omitted.

1, in the MC-CDMA system, the repeater receiver of the terminal is composed of two interference cancellation paths because two cell signals are received, and each interference cancellation path is parallel interference cancellers 110 and 210 between cells. A unit 120, 220, a despreader 130, 230, a hard determiner 140, 240, a hard decision diffuser 150, 250, and a channel estimator 160, 260.

The channel estimators 160 and 260 repeatedly update and output channel estimates using pilot symbols of a repeatedly received signal. Here, the pilot symbols corresponding to each cell are input to the channel estimators 160 and 260 through different interference cancellation paths for each cell and processed. Meanwhile, the channel estimation method used in the channel estimators 160 and 260 will be described in detail later.

The intercell parallel interference cancellers 110 and 210 receive data symbols of repeatedly received signals and repeatedly perform intercell interference cancellation. To this end, the received signal is input to each inter-cell parallel interference cancellers 110 and 210 through different interference cancellation paths for each cell signal, and each inter-cell parallel interference canceller 110 and 210 is input to the corresponding interference cancellation path. In this data symbol, interference of the cell signals other than the self cell signal is removed. Herein, the magnetic cell signal refers to a cell signal input to the interference cancellation path to which the corresponding parallel interference cancellers 110 and 210 belong. That is, referring to FIG. 1, the magnetic cell signal corresponding to the first cell path among the interference cancellation paths is the first cell signal, and the magnetic cell signal corresponding to the second cell path is the second cell signal.

On the other hand, the inter-cell parallel interference cancellers 110 and 210 spread the hard decision values output from the hard determiners 240 and 140 of the other cell signals to remove the inter-cell interferences of the other cell signals with respect to the self-cell signals. Use a value. For example, in order to mitigate signal interference of the second cell with respect to the first cell signal, a spread hard decision value corresponding to the second cell signal is used, and interference of the first cell signal with respect to the second cell signal is reduced. The spread hard decision value corresponding to the first cell signal is used to mitigate. That is, an interference signal corresponding to another cell signal may be estimated through the spread hard decision value, and inter-cell interference is mitigated by removing the estimated interference signal from signals input to the inter-cell parallel interference cancellers 110 and 210. Is output.

The equalizers 120 and 220 receive a signal in which inter-cell interference is relaxed by the inter-cell parallel interference cancellers 110 and 210, and output the channel equalized for each subcarrier signal included in the cell signal. In this case, the equalizers 120 and 220 use channel estimates generated by the channel estimators 160 and 260 for channel equalization. The channel equalized signal is outputted after orthogonality is restored. In this case, the first embodiment of the present invention uses a single tap MMSE equalizer using MMSE as a channel equalization standard, and one equalizer includes a single tap MMSE equalizer equal to the number of subcarrier signals of a corresponding cell signal.

The despreaders 130 and 230 receive signals from which the orthogonality is restored from the equalizers 120 and 220 and perform despreading and output the signals.

The hard determiners 140 and 240 hard determine a signal that is despread from the despreaders 130 and 230 and output a hard decision value. The hard decision value is a hard decision value of a self user symbol in which interference with other users in a self cell is mitigated. Here, the self user symbol means a user symbol corresponding to a repetitive receiver in a self cell signal.

The hard decision diffusers 150 and 250 redistribute the hard decision values received from the hard determiners 140 and 240 and output to the inter-cell parallel interference cancellers 110 and 210 of the other cells except for the self cells. The re-spread value of the hard decision value of the cell is used to remove the interference of the magnetic cell signal in the cell signals except for the magnetic cell.

Meanwhile, in FIG. 1, the case in which two cell signals are received by the repetitive receiver has been described as an example. However, the present invention is not intended to limit the present invention, but rather to describe embodiments of the present invention. Two or more may exist. In this case, the repeater receiver may include an interference cancellation path (parallel interference canceller, channel estimator, equalizer, despreader, hard determiner, hard decision diffuser) for each cell signal. The intercell parallel interference canceller can receive one or more hard decision values and use the intercell interference canceller.

Figure 2 is a single tab corresponding to the l-th sub-carrier signal from the equalization section 120 corresponding to a first embodiment repeats a structure diagram showing the details of the equalization unit 120 of the receiver according to the present invention, q th cell signal An example of an MMSE equalizer is shown.

Referring to FIG. 2, the equalizer 120 may include a single tap MMSE equalizer equal to the number of subcarrier signals included in the cell signal, and one single tap MMSE equalizer may include an equalization coefficient generation block 121 and an equalizer. Group 122.

The equalization coefficient generation block 121 receives the channel estimate value and the background noise variance value output from the channel estimator 160 and outputs the equalization coefficient. In this case, the background noise variance value is an experimentally calculated value. Meanwhile, a method of generating equalization coefficients in the equalization coefficient generating block 121 will be described in detail later.

On the other hand, the equalizer 122 channel-equalizes the input signal using the equalization coefficients output from the equalization coefficient generating block 121 and outputs the same.

Next, a repetitive reception method including an interference cancellation process of a terminal in an MC-CDMA system according to a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Here, a pilot symbol used for channel estimation uses a general pilot symbol without additional constraints. In the following description, an interference cancellation method is described under the assumption that accurate channel estimation is performed by the channel estimator 160, and the channel estimation method will be described in detail later. In addition, the superscript of the formula used in the following description means the sequence of repeated reception performed in the repeating receiver.

3 is a flowchart illustrating a repetitive reception method of a terminal in an MC-CDMA system according to a first embodiment of the present invention.

Here, referring to FIG. 1, a method of removing inter-cell interference with respect to a first cell signal will be described by taking a case where the cell signal to be received by the repeater receiver is a first cell signal. However, the repeater receiver according to an embodiment of the present invention performs interference cancellation not only on the self-cell signal to be received but also on all other cell signals received. The same applies to signals.

Referring to FIG. 3, the repetitive receiver receives a signal repeatedly transmitted from a plurality of cells in a multi-cell environment, and then outputs a channel estimate estimated by the channel estimator 160 using pilot symbols of the received signal (S100). ).

If the number of repetitive receptions is not the first sequence (S110), after channel estimation, the inter-cell parallel interference canceller 110 performs a hard plate of the self cell, that is, the remaining cell (second cell) signal except the first cell signal in the received signal. The inter-cell interference is mitigated using the spread value of the stationary output (S120). That is, the interference signal is estimated using the hard decision value for the remaining cells (second cell) and the estimated interference signal is removed from the received signal, thereby alleviating the interference and outputting the interference signal. On the other hand, if the number of repeated receptions is the first sequence, the inter-cell interference mitigation process using the spread hard decision value is omitted.

Subsequently, the signal in which inter-cell interference is relaxed is equalized, and channel equalization corresponding to each subcarrier is performed by the channel estimator 160 output from the channel estimator 160, and then the orthogonality is restored and output (S130). .

The orthogonality is restored and the output signal is despread through the despreader 130 and output (S140), the despread signal is input to the hard determiner 140, the interference of other users in the self-cell is reduced The hard decision value obtained by hard determining the own user symbol is used (S150).

Thereafter, the hard decision value is re-diffused through the hard decision diffuser 150 and output to the parallel interference canceller 210 of another cell (second cell). It is used to remove the interference of the cell (second cell) signal except for).

Now, the method for canceling inter-cell interference according to the first embodiment shown in FIG. 3 will be described in more detail by using a formula.

First, the method of generating equalization coefficients in the equalizer 120 will be described.

(이후, 자기 셀은 q로, 자기 셀을 제외한 다른 모든 셀은 m으로 하겠다)는 존재 하지 않으므로, 첫 번째 순차의 병렬 간섭제거기(110)는 동작하지 않는다. 그러므로 등화부(120)의 입력은

대신

이 된다. To this end, when the number of repetitive receptions of the repeating receiver is the first sequence, the hard decision value of another cell

(After this, the magnetic cell is q and all other cells except the magnetic cell will be m ). Therefore, the first-order parallel interference canceller 110 does not operate. Therefore, the input of the equalizer 120

instead

Becomes

)는 다음의 수학식 3과 같이 표현된다. Meanwhile, in the first embodiment of the present invention, as described above, MMSE is used as a channel equalization criterion. Therefore, in the first sequence, the equalization coefficient vector of the equalizer 120 (

) Is expressed by Equation 3 below.

Meanwhile, the equalizer 120 according to the first embodiment of the present invention performs channel equalization for each subcarrier, and thus has a separate equalization coefficient for each subcarrier. For example, the equalization coefficient of the first sequence of the q cell l subcarrier is calculated as in Equation 4 below, which is performed by the equalization coefficient generation block 121.

은 채널 행렬을 의미하고, 전술한 바와 같이

이 된다. here,

Means the channel matrix, as described above

Becomes

)는 다음 수학식 5와 같이 나타낼 수 있다. On the other hand, if the number of repetitive receptions of the repetitive receiver is not the first sequence, the repetitive receiver spreads the hard decision value of another cell and uses it to perform intercell interference cancellation in its cell signal. For example, from the second to the last I -sequence, the signal after the interference cancellation is performed using the hard decision value of other cells except the q- th cell, which is its own cell (

) May be expressed as in Equation 5 below.

의 확산된 신호는

이 되고, 간섭 오류는

가 된다. 따라서 수학식 5의 두 번째 등식의 첫 번째 항은 q번째 셀의 자기 신호이며, 두 번째와 세 번째 항은 오류 항 즉, 다른 셀의 간섭 신호가 된다. Where the hard decision vector of all users of the m th cell

The spread signal of

The interference error

Becomes Therefore, the first term of the second equation of Equation 5 is the magnetic signal of the q- th cell, and the second and third terms are error terms, that is, interference signals of other cells.

에 대한 등화부(120)의 계수 벡터를 나타낸 것이다.As described above, the signal from which the interference is removed by the inter-cell parallel interference canceller 110 is input to the equalizer 120 to be equalized and output after the channel is equalized. Here, the equalization coefficient to be used can be obtained as shown in Equation 6 below. Equation 6 below is a signal after interference cancellation of the q- th cell as in Equation 5 described above.

The coefficient vector of the equalizer 120 with respect to FIG.

Meanwhile, since channel equalization is performed for each subcarrier of each cell, one equalizer 120 includes a single tap MMSE equalizer equal to the number of subcarriers L. Therefore, the above equation may be obtained as an equalization coefficient for each subcarrier by the equalization coefficient generating block 121 of the single tap MMSE equalizer. Equation 7 below is an example of an equalization coefficient corresponding to the l- th subcarrier signal among q- th cell signals, and the same applies to other subcarrier signals.

은 잔여 셀 간 간섭이 충분히 작아지는 반복 수신의 순차에서는 병렬 간섭제거가 완벽하다는 가정 하에서 제외가 가능하다. Comparing the above coefficient with Equation 4, the variance of the interfering signal between the remaining cells of the l- th subcarrier signal of all other cells except the q- th cell, where all other cells are denoted by m .

Can be excluded under the assumption that parallel interference cancellation is perfect in a sequence of repeated receptions where the residual inter-cell interference is sufficiently small.

Therefore, the equalization coefficient of the q cell l subcarrier after the specific sequence j of repetitive reception can be obtained as in Equation 8 below.

항을 등화 계수 산출식에 제외하고서 등화 계수를 산출하면, 수학식 4를 이용한 등화 계수 산출 방법에 비해 복잡도가 감소하므로, 등화부(120)의 추가적인 성능 개선을 기대할 수 있다. As the inter-cell interference of other cells is sufficiently small when high-order repetitive reception is made, as shown in Equation 8, the dispersion of the interference signal between residual cells

When the equalization coefficient is calculated by excluding the term from the equalization coefficient calculation equation, since the complexity is reduced compared to the equalization coefficient calculation method using Equation 4, further performance improvement of the equalization unit 120 can be expected.

FIG. 4 is a flowchart illustrating an example of a process of despreading, hard determining, and respreading according to a first embodiment of the present invention. Next, a signal flow after channel equalization will be described.

을 역확산기(130)에 의해 역 확산된 신호(

)와, 이를 경성 판정한 경성 판정치(

)를 나타낸다. Since channel equalization is performed for each subcarrier, the equalizer 120 may include L single tap MMSE equalizers to channel equalize L subcarriers. The following equation (9) is equalized by the equalizer L single tap MMSE of the L-dimensional output signal vector

Is despread by the despreader 130 (

) And the hard decision value (

).

는 경성판정기(140)에서 수행되는 경성 판정 방법을 나타낸다. 또한, 도 4에 도시된 코드 행렬

의 k번째 열 벡터는 k번째 사용자의 확산코드와 q번째 셀의 스크램블 코드가 곱해진 벡터로 이루어진다. 전술한 과정을 통해 산출 된경성 판정치

는 다음 i+1차 반복 수신을 위해 사용된다. here,

Denotes a hard determination method performed by the hard determiner 140. Also, the code matrix shown in FIG. 4

The k th column vector of is composed of a vector obtained by multiplying the k th user's spreading code by the q th cell's scramble code. Hardness judgment value calculated through the above process

Is used for the next i + 1st iterative reception.

을 다음의 수학식 10과 같이 재 확산하여 출력한다. Thereafter, the repeater receiver receives the hard decision value through the hard decision diffuser 150.

And re-diffusion is output as shown in Equation 10 below.

를 확산시킨 신호

는 자기 셀을 제외한 나머지 다른 셀

의 셀 간 병렬 간섭제거기(210)로 입력되어 셀 간 간섭을 제거하는데 사용된다. 전술한 바와 같이 자기 셀을 제외한 다른 셀의 경성 판정치를 이용한 셀 간 간섭제거 방법은 셀 간 간섭을 효과적으로 완화하면서도 경성 판정치를 사용하여 셀 간 간섭을 제거함으로써 임의의 확산요소의 차원을 갖는 행렬의 역을 매 심볼마다 계산해야 하는 기존의 간섭 제거 방법에 비해 복잡도는 낮추는 효과가 있다. Hard decision value as above

Spread signal

Is any other cell except magnetic

It is input to the inter-cell parallel interference canceller 210 is used to remove the inter-cell interference. As described above, the inter-cell interference cancellation method using the hard decision value of other cells except for the self cell effectively mitigates the inter-cell interference, while removing the inter-cell interference using the hard decision value, and thus has a matrix having an arbitrary spreading element dimension. Compared to the conventional interference cancellation method, in which the inverse is to be calculated for every symbol, the complexity is reduced.

Meanwhile, in the above-described first embodiment, a method for canceling intercell interference has been described under the assumption that accurate channel estimation is performed. But In an Orthogonal Frequency Division Multiplexing (OFDM) system including a downlink MC-CDMA system, if the channel estimation is not accurate, the performance of a repeating receiver considering inter-cell interference does not consider inter-cell interference. Rather, the reception performance may be lower than that of the receiver.

Therefore, the following describes a method of improving performance using the channel estimation method according to an embodiment of the present invention using an expectation maximization (EM) algorithm.

As described above, a channel estimation method using pilot symbols may be divided into an insertion method in a time domain and a frequency domain. In the exemplary embodiment of the present invention, pilot symbol insertion in the time domain is described as an example.

FIG. 5 is a structural diagram illustrating a channel estimator 160 according to a first embodiment of the present invention, and illustrates a channel estimator 160 performing channel estimation using a hard decision value.

Referring to FIG. 5, the channel estimator 160 repeatedly performs channel estimation whenever the repeater receiver receives a signal, and uses the hard decision value of the previous received signal. In such a channel estimation method, it is possible to calculate a more accurate channel estimate by repeatedly updating the channel estimate.

FIG. 6 is a flowchart illustrating a channel estimation method using an EM algorithm during an iterative reception process according to a first embodiment of the present invention, and uses hard decision values for accurate channel estimation.

First, in order to estimate the channel using the EM algorithm, an initial value of a symbol vector used for channel estimation is required. When the number of repeated receptions is the first sequence (S200), the repeating receiver configures an initial symbol vector (S210). Afterwards, whenever repeated reception is performed, the channel estimator 160 updates the symbol vector using the redistributed signal of the hard decision value generated from the previous received signal (S220).

Subsequently, an initial symbol vector or an updated symbol vector is then used to obtain a channel impulse response estimate (S230). Meanwhile, the generated channel impulse response estimate is a value corresponding to the time domain, and it is necessary to convert the channel impulse response estimate to the frequency domain in order to obtain a channel estimate as a final result value. Accordingly, the channel impulse response estimate is converted into the frequency domain to be a channel frequency response estimate (S250), and as a result, the channel frequency response estimate is a channel estimate.

This channel estimation method is repeatedly performed until the number of times of repeated reception becomes the final sequence in order to obtain an accurate channel estimate (S250).

Now, the channel estimation method according to the first embodiment of the present invention shown in FIG. 6 will be described in more detail using equations.

대신, 벡터

를 사용한다. Meanwhile, the following description will be given of an example of channel estimation for a magnetic cell, but the same may be applied to channel estimation of not only the magnetic cell but also other cells. Therefore, in the following description, the subscript q indicating the order of the cell is excluded. In addition, the channel frequency response matrix

Instead, vector

Use

라 놓으면, 채널 주파수 반응 추정치와 채널 임펄스 반응 추정치는

의 관계가 성립된다. 여기서, LㅧN 행렬

는 채널 주파수 반응 추정치를 구하기 위한 이산 퓨리에 변환(Discrete Fourier Transform, DFT) 행렬로서 다음과 같이 나타낼 수 있다. Accordingly, the N- dimensional vector corresponding to the channel impulse response estimate is calculated.

, The channel frequency response estimate and the channel impulse response estimate

Relationship is established. Where L ㅧ N matrix

Is a Discrete Fourier Transform (DFT) matrix for obtaining a channel frequency response estimate.

을 이용한 최대우도 추정치를 이용하는 최대우도 채널 추정 방법은 다음의 수학식 11과 같이 이뤄진다. Meanwhile, given by Equation 2

The maximum likelihood channel estimation method using the maximum likelihood estimation value is performed as shown in Equation 11 below.

는 채널 임펄스 반응 추정치

에 대한 수신 신호

의 우도함수(likelihood function)로서, 이 함수의 비선형성으로 인해 최대우도 추정치를 구하는 것이 매우 어렵다. 그러나 본 발명의 실시 예 EM 알고리즘을 적용하여 최대우도 추정치를 보다 용이하게 구할 수 있다. here,

Estimates channel impulse response

Received signal for

As the likelihood function of, it is very difficult to find the maximum likelihood estimate due to the nonlinearity of this function. However, the maximum likelihood estimate can be more easily obtained by applying the embodiment EM algorithm of the present invention.

은 수학식 12과 같이 재 표현할 수 있다. Received Signal of Equation 2 for Application of EM Algorithm

Can be reexpressed as in Equation 12.

이고, 이 심볼 행렬의 심볼 벡터 형태는

이다. 이때, EM 알고리즘의 적용을 위해서는 수학식 12에 의해 주어진 수신 신호

을 관찰되는 불완전한 데이터로 놓고, 검출하고자 하는 심볼

를 관찰되지 않은 데이터로 놓으면

를 완전한 데이터로 놓을 수 있다. 이에 따른, EM 알고리즘은 다음과 같이 구성된다. Where symbol matrix

The symbol vector form of this symbol matrix is

to be. At this time, in order to apply the EM algorithm, the received signal given by Equation 12

Is the incomplete data observed and the symbol to be detected

If you put the as unobserved data

Can be set to complete data. Accordingly, the EM algorithm is configured as follows.

뿐만 아니라 검출하고자 하는 심볼

도 주어진다는 가정 하에 채널 임펄스 반응 추정치

를 추정하기 위한 우도함수(

)를 구하는 기대 단계는 다음의 수학식 13로 표현된다. First, the received signal

As well as the symbols to be detected

Channel impulse response estimate under the assumption

Likelihood function for estimating

Expected step to find is expressed by the following equation (13).

를 최대화 시키는 최대화 단계는 다음의 수학식 14과 같이 표현된다. Later, the likelihood function obtained at the expected stage

The maximizing step of maximizing is expressed by Equation 14 below.

이며, 이전(p번째) 수신 신호의 경성 판정치에 의해 갱신된다. 채널 임펄스 반응 추정치로부터 주파수 도메인으로 변환되어 산출되는 주파수 도메인의 채널 임펄스 반응 추정치(

)의 결과 식은 다음의 수학식 15와 같이 표현이 가능하다. Where symbol vector

Is updated by the hard decision value of the previous ( p- th) received signal. An estimate of the channel impulse response in the frequency domain, which is calculated by transforming the channel impulse response estimate from the

) Can be expressed as in Equation 15 below.

는 이전(p번째) 순차의 반복 수신 과정에서 경성 판정치의 재확산된 심볼로 구성된 대각 행렬이다. 이 때, 위의 채널 임펄스 반응 추정치(

)를 이용하여 채널 주파수 반응 추정치(

)는 다음의 수학식 16과 같이 구해진다. here,

Is a diagonal matrix consisting of the respread symbols of the hard decision value in the previous ( p- th) iterative reception process. At this time, the above channel impulse response estimate (

) To estimate channel frequency response (

) Is obtained as in Equation 16 below.

)는 결과적으로 채널 추정기(160)의 출력인 채널 추정치가 되며, 이는 셀 간 병렬 간섭제거기(110)로 입력된다. The channel frequency response estimates obtained as described above (

) Results in a channel estimate that is the output of channel estimator 160, which is input to intercell parallel interference canceller 110.

Meanwhile, for channel estimation using the EM algorithm, as described above, an initial symbol vector used for channel estimation is required, and an initial value of the symbol vector may be obtained as in Equation 17 below.

는 파일럿 부반송파의 위치에 파일럿 심볼이 들어가고, 그 외 부반송파의 위치에는 영으로 구성된 초기치 벡터이다. EM 알고리즘의 성능은 초기치 벡터에 의해 큰 영향을 받는다. 그러므로 더 좋은 채널 추정치를 얻기 위해서는 더욱 촘촘한 파일럿 심볼이 필요하다. 채널 추정기(160)는 상기의 초기 심볼 벡터의 구성을 시작으로 전술한 바와 같이 채널 추정 동작을 최종 순차까지 반복하여 채널 주파수 반응 추정치, 즉 채널 추정치를 보다 정확하게 구할 수 있다. here,

Is an initial value vector composed of pilot symbols at the position of pilot subcarriers and zero at the position of other subcarriers. The performance of the EM algorithm is greatly affected by the initial vector. Therefore, more precise pilot symbols are needed to obtain better channel estimates. The channel estimator 160 can more accurately obtain the channel frequency response estimate, that is, the channel estimate, by repeating the channel estimation operation to the final sequence as described above, starting with the configuration of the initial symbol vector.

Meanwhile, in the above-described first embodiment, an interference cancellation method and a repetitive receiver for removing only inter-cell interference have been described. In the following, inter-cell user symbol interference in a mobile communication system according to the second embodiment of the present invention will now be described. And a repeated reception method for canceling inter-cell interference and a repeating receiver performing the same. In the following description, interference between user symbols in a cell is referred to as intra-cell interference.

Next, an MC-CDMA system will be described with reference to an iterative receiver for removing intra-cell interference and inter-cell interference in a mobile communication system according to a second embodiment of the present invention.

On the other hand, the repeater receiver according to the second embodiment of the present invention includes the same components as the first embodiment described above, and the same reference numerals are used for the same components. In addition, in the second embodiment of the present invention, repeated description of the same components as the above-described repeating receiver of the first embodiment will be omitted.

FIG. 7 is a structural diagram illustrating a repetitive receiver in an MC-CDMA system according to a second embodiment of the present invention and is a repetitive receiver considering not only intercell interference cancellation but also intracell interference cancellation.

As shown in FIG. 7, the repeater receiver in a multi-cell environment includes one or more inter-cell parallel interference cancellers 110 and 210, equalizers 120 and 220, despreaders 130 and 230, and hard determiner 140. , 240, hard decision diffusers 150, 250, and channel estimators 160, 260, and may further include intra-cell parallel interference cancellers 170, 270.

The channel estimators 160 and 260 perform channel estimation using pilot symbols of their cell signals. In this case, the channel estimators 160 and 260 repeatedly perform channel estimation whenever the signal is repeatedly received in order to perform more accurate channel estimation.

The inter-cell parallel interference cancellers 110 and 210 perform the same functions as the inter-cell parallel interference cancellers 110 and 210 of the first embodiment described above, and the output of the inter-cell parallel interference cancellers 110 and 210 is parallel within the cell. It is input to the interference cancellers 170 and 270.

The intra-cell parallel interference cancellers 170 and 270 receive a signal from which inter-cell interference has been removed from the inter-cell parallel interference cancellers 110 and 210 and correspond to a magnetic cell signal in the signal from which the inter-cell interference is removed and output. The spread hard decision value is used to eliminate intra-cell interference. That is, using the spread hard decision value corresponding to the self-cell signal, the intra-cell interference signal corresponding to the remaining users except for the user corresponding to the repeating receiver is estimated, and the self-cell signal from which the inter-cell interference is removed is estimated. The interference signal in the cell is removed and output.

The signals output from the intra-cell interference cancellers 170 and 270 are input to the hard determiners 140 and 240 through the equalizers 120 and 220 and the despreaders 130 and 230. Thereafter, the hard determiners 140 and 240 calculate a hard decision value based on this, and the hard decision diffusers 150 and 250 diffuse the hard decision values again to inter-cell parallel interference cancellers 210 and 110 and the cells. Output to parallel interference cancellers 170 and 270. At this time, the spread signal of the hard decision value is input to the intra-cell parallel interference cancellers 170 and 270 of the magnetic cell and the inter-cell parallel interference cancellers 210 and 110 of the remaining cells except the magnetic cell.

Next, an iterative reception method of a terminal including an intracell interference and an intercell interference cancellation process according to the second embodiment will be described with reference to the accompanying drawings.

8 is a flowchart illustrating a method for repeatedly receiving a UE repeatedly in a MC-CDMA system according to a second embodiment of the present invention, and includes an intracell interference and an intercell interference cancellation process.

Referring to FIG. 8, the iterative receiver repeatedly performs channel estimation on the received signal repeatedly received in a multi-cell environment through the channel estimator 160 and outputs a channel estimate (S300).

On the other hand, when the number of repeated receptions is the first sequence, there is no hard decision value. Therefore, the repetitive receiver removes and outputs inter-cell interference through the inter-cell parallel interference canceller 210 only when the number of repetitive receptions is not the first sequence (S310). At this time, the inter-cell parallel interference canceller 210 removes interference of other cell signals by using spread values of hard decision values of other cell signals. The signal in which the inter-cell interference is relaxed is inputted to the intra-cell parallel interference canceller 170 again, and interference cancellation of another user signal in the self-cell signal using the hard decision spread signal of the self-cell is performed (S330).

If the number of repeated receptions is the first sequence, since the hard decision value does not exist, the above-described intra-cell and inter-cell interference cancellation process is omitted.

Subsequently, as described above, the signal in which the inter-cell and inter-cell interference is relaxed by the inter-cell parallel interference canceller 110 and the intra-cell parallel interference canceller 170 is channel-equalized by the equalizer 120 to restore orthogonality. (S340).

The signal equalized by the channel equalizer from the equalizer 120 and the orthogonality is restored is despread through the despreader 130 and outputted (S350). Thereafter, the despread signal is input to the hard determiner 140 again and used to calculate a hard decision value of the hard user symbol in which interference of other users in the self cell is mitigated (S360).

Then, the hard decision value is re-diffused through the hard decision diffuser 150 and outputted to the inter-cell parallel interference canceller 210 of another cell and the intra-cell parallel interference canceller 170 of the other cell, and thus the hard decision value of each cell. The redistributed value is used to remove intra-cell and inter-cell interference.

Now, the repeated reception method according to the second embodiment of the present invention shown in FIG. 8 will be described in more detail by using a mathematical formula.

Meanwhile, the interference cancellation process according to the second embodiment of the present invention performs a process similar to the intercell interference cancellation process according to the first embodiment described above, and the intercell interference cancellation process according to the first embodiment described above. Similar parts are omitted from the description.

First, when the number of repeated receptions is the first sequence, not only inter-cell interference cancellation but also intra-cell interference cancellation are not performed. As in the above-described first embodiment, data symbols are input to the equalizer 120 without interference cancellation.

Therefore, only the interference cancellation of the ith sequence except the first sequence will be described below.

)가 수학식 5와 같이 셀 간 간섭제거만을 고려하였다면, 본 발명의 제2 실시 예에서는 q번째 셀을 제외한 다른 셀의 경성 판정치와 셀 내 k번째 사용자를 제외한 다른 사용자의 경성 판정치를 이용하여 다음의 수학식 18과 같이 q번째 셀 k번째 사용자의 i번째 순차 의 병렬 간섭제거가 수행된다. In the above-described first embodiment, the signal input to the equalizer 120 (

) Considers only inter-cell interference cancellation as shown in Equation 5, the second embodiment of the present invention uses the hard decision value of the other cell except the q- th cell and the hard decision value of the other user except the k- th user in the cell As shown in Equation 18, parallel interference cancellation of the i th sequence of the k th user of the q th cell is performed.

이고, 두 번째와 세 번째 항 그리고 네 번째 항은 셀 내 간섭 및 셀 간 간섭에 대응되는 오류 항이 된다. 이와 같이 수학식 18의 두 번째 등식의 두 번째 항은 k번째 사용자를 제외한 다른 사용자 신호에 의한 간섭 신호로서, 셀 내 병렬 간섭제거기(172)에 의해 제거되는 오류 항이다. here,

The second, third and fourth terms are error terms corresponding to intra-cell interference and inter-cell interference. As described above, the second term of the second equation of Equation 18 is an interference signal caused by other user signals except for the k- th user, and is an error term removed by the intra-cell parallel interference canceller 172.

9 illustrates a process of removing intra-cell interference and inter-cell interference according to a second embodiment of the present invention.

,

가 존재 하지 않으므로, 첫 번째 순차의 병렬 간섭제거기는 동작하지 않는다. 따라서 q셀 l부반송파의 첫 번째 순차의 등화 계수 벡터는 수학식 4와 동일하다. For a repeating receiver that performs intracell interference and intercell interference cancellation, as described above, the hard decision value in the first sequence

,

Does not exist, the first sequential parallel interference canceller does not work. Therefore, the equalization coefficient vector of the first sequence of the q cell l subcarrier is equal to Equation 4.

On the other hand, the repeated reception operation after the second sequence is as follows.

는 수학식 11에서처럼 셀 내 간섭 즉, 셀 내의 다른 사용자로 인한 간섭이 제거된 신호이므로 이 신호에 대한 채널 등화는 사용자마다 달라지는 것이다. 이에 따라, i번째 순차의 경성 판정치를 이용한 셀 내 간섭 및 셀 간 간섭제거 후의 신호

에 대한 등화부(120)의 등화 계수 벡터(

)는 다음의 수학식 19와 같이 구할 수 있다. In the repetitive receiver according to the first embodiment described above, the equalization coefficients of the users in their cells for channel equalization are the same. However, in the channel equalization of the repeater receiver according to the second embodiment of the present invention which simultaneously performs intra-cell interference and inter-cell interference cancellation, a different single tap MMSE equalizer is used for each user as illustrated in FIG. 7. The reason is the signal after the intercell and intercell interference cancellation

Since Equation 11 eliminates intra-cell interference, that is, interference caused by other users in the cell, the channel equalization for the signal is different for each user. Accordingly, the signal after the intra-cell interference and the inter-cell interference cancellation using the i -sequential hard decision value

Equalization coefficient vector of equalizer 120 for

) Can be obtained as in Equation 19 below.

)는 등화 계수 생성블록(121)에서 다음의 수학식 20과 같이 주어진다. Also, the equalization coefficient of the single-tap MMSE equalizer corresponding to q cell k user l subcarrier (

) Is given by Equation 20 in the equalization coefficient generation block 121.

과 m번째 셀 신호의 l부반송파 신호의 잔여 셀 간 간섭신호의 분산

은 셀 간 간섭이 충분히 작아지는 반복 수신의 순차에서는 제외할 수 있다. 따라서 실험적으로 주어지는 반복 수신의 특정 순차 j이후의 등화 계수는 등화 계수 생성블록(121)에 의해 다음의 수학식 21과 같이 구해진다. As in the first embodiment described above, the dispersion of the interference signal in the remaining cells of the l subcarrier signal corresponding to the k th user of the q th cell signal

Variance of the interfering signal between the remaining cells of the l subcarrier signal of the mth cell signal

Can be excluded from the sequence of repeated reception where the inter-cell interference becomes sufficiently small. Therefore, equalization coefficients after a specific sequence j of repeated reception experimentally given are obtained by the following equation 21 by the equalization coefficient generation block 121.

The equalization coefficient generation method using Equation 21 can be expected to further improve performance compared to the equalizer using the coefficients of Equation 20 in the higher-order iterative reception stage as in the first embodiment.

Meanwhile, since the channel estimation method and the despreading of the signal from which the intra-cell interference and the inter-cell interference are removed and the re-spreading of the hard decision value are performed in the same manner as in the above-described first embodiment, description thereof will be omitted. However, the channel estimate calculated by performing channel estimation in the channel estimator is input only to the inter-cell parallel interference canceller 210 in the first embodiment of the present invention, but the first-cell inter-cell parallel interference canceller 210 of the present invention is performed. In addition, it is also input to the parallel interference canceller 170 in the cell.

The repeated reception method and the repeated receiver in the multi-cell environment according to the second embodiment of the present invention effectively remove intra-cell interference and inter-cell interference by using the hard decision value of the own cell signal and the hard decision value of another cell. Intra-cell or inter-cell interference can be eliminated. In addition, it is possible to obtain a more accurate channel estimate by using the hard decision value of the self cell signal for channel estimation by updating the channel estimate every time it is repeatedly received.

An embodiment of the present invention is not implemented only through the above-described apparatus and / or method, but through a program for realizing a function corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded, and the like. This implementation may be easily implemented by those skilled in the art to which the present disclosure pertains based on the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the range.

Repeated reception method and repeater receiver in a mobile communication system according to an aspect of the present invention can remove inter-cell interference in a multi-cell environment by using hard decision values corresponding to signals received from cells other than its own. . In addition, the hard decision value of the signal received from the own cell may be used to eliminate intra-cell interference with the own user signal. Therefore, compared to the conventional interference cancellation method in which the inverse of a matrix having a dimension of an arbitrary spreading element is calculated every symbol, it is possible to effectively remove intra-cell interference and inter-cell interference while reducing the complexity of the implementation method.

In addition, a more accurate channel estimate can be obtained by iteratively updating the channel estimate using the hard decision value of the previous sequential received signal, thereby improving the reception performance of the repeating receiver.

Claims (14)

A reception method in which a receiver repeatedly receives a reception signal including a first cell signal and at least one other cell signal in a multi-cell environment, Hard determining each cell signal included in the received signal and outputting a hard decision value corresponding to each cell signal; And Estimating the inter-cell interference signal using the remaining hard decision values other than the hard decision value corresponding to the first cell signal among the hard decision values, and removing the inter-cell interference signal from the received signal. Repeated reception method comprising a. The method of claim 1, Intra-cell interference signals corresponding to remaining users other than the user corresponding to the receiver are estimated using the hard decision value corresponding to the first cell signal, and the intra-cell interference signal is received from the received signal from which inter-cell interference has been removed. Steps to remove Repeated receiving method characterized in that it further comprises. The method according to claim 1 or 2, Performing channel estimation on each cell signal included in the received signal and outputting a channel estimate corresponding to each cell signal; And Performing channel equalization for each cell signal included in the received signal using the channel estimate More, Outputting the hard decision value, And hardly determining each cell signal on which the channel equalization has been performed and outputting the hard decision value. The method of claim 3, wherein Performing the channel equalization, Generating an equalization coefficient by using a minimum mean square error (MMSE) equalization algorithm for each subcarrier signal included in each cell signal; And Channel equalizing and outputting a subcarrier signal corresponding to the equalization coefficient using the equalization coefficient Repeated reception method comprising a. The method of claim 3, wherein The outputting of the channel estimate may include: Updating a symbol vector used for channel estimation using the hard decision value; Updating a channel impulse response estimate using the symbol vector; And Converting the channel impulse response estimate into a frequency domain and outputting the channel estimate Repeated reception method comprising a. The method of claim 5, Updating the channel impulse response estimate, Calculating a likelihood function for updating the channel impulse response estimate using an expectation maximization (EM) algorithm; And Updating the channel impulse response estimate using the hard decision value and the likelihood function Repeated reception method comprising a. The method of claim 4, wherein And the equalization coefficient is calculated using a signal from which interference between cells is removed for each cell signal as the received signal is repeatedly received. The method of claim 1, And a subcarrier corresponding to the receiver is allocated to the same position in both the first cell signal and at least one other cell signal. The method of claim 1, And the received signal comprises a control channel for broadcasting a modulation scheme of the first cell signal and at least one other cell signal. A repeating receiver for repeatedly receiving a received signal including a first cell signal and at least one second cell signal in a multi-cell environment, A first hard determiner for hard determining the second cell signal and outputting a first hard decision value; And An inter-cell parallel interference canceller for estimating the inter-cell interference signal using the first hard decision value and removing the inter-cell interference signal from the received signal Repeating receiver comprising a. The method of claim 10, A second hard determiner for hard determining the first cell signal and outputting a second hard decision value; And Estimating an intra-cell interference signal corresponding to a user other than the user corresponding to the repeating receiver using the second hard decision value, and removing the intra-cell interference signal from a signal output from the inter-cell parallel interference canceller. In-cell parallel interference canceller Repeater receiver, characterized in that it further comprises. The method of claim 11, A channel estimator for channel estimation based on the first cell signal and outputting a channel estimate; And An equalizer for performing channel equalization on the first cell signal using the channel estimate and outputting the channel equalized first cell signal to the second hard determiner Repeater receiver, characterized in that it further comprises. The method of claim 12, The equalizing unit, A single tap minimum mean square error (MMSE) equalizer equal to the number of subcarrier signals included in the first cell signal, The single tap minimum mean squared error equalizer, An equalization coefficient generation block generating an equalization coefficient corresponding to one subcarrier signal among a plurality of subcarrier signals included in the first cell signal; And An equalizer for channel equalizing and outputting a subcarrier signal corresponding to the equalization coefficient by using the equalization coefficient Repeating receiver comprising a. The method of claim 12, The channel estimator, Each time the reception of the received signal is repeated, the channel estimation is performed using the second hard decision value, and an expected maximum (EM) algorithm is used for the channel estimation.

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